Obesity is a major public health concern because of its increasing prevalence and associated health risks. Obesity and overweight are generally defined by body mass index (BMI), which is correlated with total body fat and estimates the relative risk of disease. BMI is calculated by weight in kilograms divided by height in meters squared (kg/m2). Overweight is typically defined as a BMI of 25–29.9 kg/m2, and obesity is typically defined as a BMI of 30 kg/m2. See, e.g., National Heart, Lung, and Blood Institute, Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, The Evidence Report, Washington, D.C.: U.S. Department of Health and Human Services, NIH publication no. 98-4083 (1998).
The increase in obesity is of concern because of the excessive health risks associated with obesity, including coronary heart disease, strokes, hypertension, type 2 diabetes mellitus, dyslipidemia, sleep apnea, osteoarthritis, gall bladder disease, depression, and certain forms of cancer (e.g., endometrial, breast, prostate, and colon). The negative health consequences of obesity make it the second leading cause of preventable death in the United States and impart a significant economic and psychosocial effect on society. See, McGinnis M, Foege W H., “Actual Causes of Death in the United States,” JAMA, 270, 2207–12 (1993).
Obesity is now recognized as a chronic disease that requires treatment to reduce its associated health risks. Although weight loss is an important treatment outcome, one of the main goals of obesity management is to improve cardiovascular and metabolic values to reduce obesity-related morbidity and mortality. It has been shown that 5–10% loss of body weight can substantially improve metabolic values, such as blood glucose, blood pressure, and lipid concentrations. Hence, it is believed that a 5–10% intentional reduction in body weight may reduce morbidity and mortality.
Currently available prescription drugs for managing obesity generally reduce weight by inducing satiety or decreasing dietary fat absorption. Satiety is achieved by increasing synaptic levels of norepinephrine, serotonin, or both. For example, stimulation of serotonin receptor subtypes 1b, 1d, and 2c and 1- and 2-adrenergic receptors decreases food intake by regulating satiety. See, Bray G A, “The New Era of Drug Treatment. Pharmacologic Treatment of Obesity: Symposium Overview,” Obes Res., 3(suppl 4), 415s–7s (1995). Adrenergic agents (e.g., diethylpropion, benzphetamine, phendimetrazine, mazindol, and phentermine) act by modulating central norepinephrine and dopamine receptors through the promotion of catecholamine release. Older adrenergic weight-loss drugs (e.g., amphetamine, methamphetamine, and phenmetrazine), which strongly engage in dopamine pathways, are no longer recommended because of the risk of their abuse. Fenfluramine and dexfenfluramine, both serotonergic agents used to regulate appetite, are no longer available for use.
More recently, CB1 cannabinoid receptor antagonists/inverse agonists have been suggested as potential appetite suppressants. See, e.g., Arnone, M., et al., “Selective Inhibition of Sucrose and Ethanol Intake by SR141716, an Antagonist of Central Cannabinoid (CB1) Receptors,” Psychopharmacol, 132, 104–106 (1997); Colombo, G., et al., “Appetite Suppression and Weight Loss after the Cannabinoid Antagonist SR141716,” Life Sci., 63, PL113–PL117 (1998); Simiand, J., et al., “SR141716, a CB1 Cannabinoid Receptor Antagonist, Selectively Reduces Sweet Food Intake in Marmose,” Behav. Pharmacol., 9, 179–181 (1998); and Chaperon, F., et al., “Involvement of Central Cannabinoid (CB1) Receptors in the Establishment of Place Conditioning in Rats,” Psychopharmacology, 135, 324–332 (1998). For a review of cannabinoid CB1 and CB2 receptor modulators, see Pertwee, R. G., “Cannabinoid Receptor Ligands: Clinical and Neuropharmacological Considerations, Relevant to Future Drug Discovery and Development,” Exp. Opin. Invest. Drugs, 9(7), 1553–1571 (2000).
Although investigations are on-going, there still exists a need for a more effective and safe therapeutic treatment for reducing or preventing weight-gain.
In addition to obesity, there also exists an unmet need for treatment of alcohol abuse. Alcoholism affects approximately 10.9 million men and 4.4 million women in the United States. Approximately 100,000 deaths per year have been attributed to alcohol abuse or dependence. Health risks associated with alcoholism include impaired motor control and decision making, cancer, liver disease, birth defects, heart disease, drug/drug interactions, pancreatitis and interpersonal problems. Studies have suggested that endogenous cannabinoid tone plays a critical role in the control of ethanol intake. The endogenous CB1 receptor antagonist SR-141716A has been shown to block voluntary ethanol intake in rats and mice. See, Arnone, M., et al., “Selective Inhibition of Sucrose and Ethanol Intake by SR141716, an Antagonist of Central Cannabinoid (CB1) Receptors,” Psychopharmacol, 132, 104–106 (1997). For a review, see Hungund, B. L and B. S. Basavarajappa, “Are Anandamide and Cannabinoid Receptors involved in Ethanol Tolerance? A Review of the Evidence,” Alcohol & Alcoholism. 35(2) 126–133, 2000.
Current treatments for alcohol abuse or dependence generally suffer from non-compliance or potential hepatotoxicity; therefore, there is a high unmet need for more effective treatment of alcohol abuse/dependence.